1. Field of the Invention
The present invention relates to a route searching method and system, and navigation apparatus in which route searching is performed based on a preference parameters calculated as road usage frequencies, representing preference degrees, according to preference items which can be factors for route selection.
2. Description of the Related Art
Probe cars have often been used to search for recommendable routes for vehicle drivers. Such probe cars are vehicles in which various devices including sensors and communication devices are installed and each of which collects data (herein after referred to as “probe data”) such as vehicle location, vehicle traveling speed, travel distance, and route information and transmits the collected probe data to a predetermined traffic information center. There are many cases in which taxis are used as probe cars with a support of a taxi company or in which private vehicles are used as probe cars, based on contracts concluded with users, as part of a traffic information service for private vehicles.
For car navigation apparatuses, a route searching function for finding an optimum route to a destination is indispensable. Generally, in route searching, a route from a departure place to a destination requiring a minimum amount of travel time or requiring a minimum distance to be traveled is determined. A route determined as a result of route searching, however, may include a road which is seldom traveled even by local residents, for example, because the road is too narrow or includes many blind turns. Hence, route searching is required to take into consideration not only time and distance but also ease and safety of driving.
In JP-A No. H09-287968, a route searching method using vehicle travel trajectory is disclosed. In the method, route searching is performed with greater priority placed on more often traveled roads.
In JP-A No. 2004-333377, a route searching method in which commercial-vehicle travel counts are used is disclosed as a method capable of finding routes offering greater convenience, for example, ease and safety of driving. In the method, route searching is carried out so that road links on which commercial vehicle weighting exceeds a certain value are included in the route to be determined. Thus, this method makes use of commercial vehicle drivers' know-how for route selection.
According to the invention of JP-A No. H09-287968, route searching is performed based on travel trajectory of the probe car. Therefore, when a road does not exist in the travel trajectory, the conventional route is adopted. Even in cases in which roads provided with travel trajectory of the probe car are available, they cannot be reflected in a route to be determined unless the driver does not know the roads are easy and safe to travel.
In the invention of JP-A No. 2004-333377, road links frequently used by commercial vehicles are selected based on commercial vehicle travel trajectory. This results in biased route searching, that is, the route recommended as being optimum as a result of route searching always includes road links frequently used exclusively by commercial vehicles. When a commercial vehicle driver selects a route, the driver's selection is likely affected, for example, by business purposes, jurisdiction, or quota, so that the selected route is not necessarily easy and safe to travel. Different people prefer different routes with their preference affected, for example, by vehicle type, travel purpose (commuting, shopping, leisure, etc.), travel distance (time requirement), and driver gender and age. According to the invention of JP-A No. 2004-333377, behavioral inclinations of different types of drivers are not considered, so that finding a route meeting various preference of individual drivers is difficult.
The present invention has been made in view of the above problems with the known route searching methods, and an object of the present invention is to provide a route searching method, a route searching system, a center apparatus and an in-vehicle terminal apparatus which make it possible to find an easy and safe to drive, highly convenient route by making use of many pieces of general probe data so as to share the preference parameters which comprises the route searching know-how of general drivers having similar travel purposes and preferences to those of the own vehicle driver.